>This means that global variables, dynamic variables (variable-variables, variable function calls, etc) and references are not allowed.<p>Globals, sure, bad practice. Ideally we wouldn't have any. Dynamic variables make sense to exclude, it turns static analysis into the halting problem. Luckily they're a bad practice too since 5.3 introduced closures.<p>But <i>references</i>?<p><i></i>EDIT<i></i>: It's by Anthony Ferrara! and some other pretty big names in the PHP community